Magnetic cards with magnetic stripes formed as recording medium on name card size cards are now widely in use in banks as well as in the so-called "credit" field as personal ID (identifying) cards. Such magnetic cards, however, have rather limited uses due to their small storage capacity. This small capacity also limits their identifying capability, hence taking away from their usefulness and safety.
Recently, however, studies have been made about the possibility of IC cards and optical cards being used with lager storage capacity.
The optical card has an extremely large storage capacity, being capable of recording about of 1-200 M bytes, which is more than enough for a personal data memory. And the magneto-optical card, a kind of optical card, is capable of re-writing information unlike the optical card for reproduction or additional storage type, and is expected to be useful in wider and more diversified fields.
This magneto-optical card is composed of a card and a layer of magneto-optical recording medium formed thereon. The latter consists of a vertically magnetized film. With this magneto-optical card, recording of information is done by irradiation with laser beam having a biased magnetic field being applied from outside. As the magneto-optical recording medium irradiated with the laser beam is heated to a predetermined temperature, the magneto-optical recording medium is magnetized in the direction of the biased magnetic field as it is cooled thereafter. Hence, recording of given information becomes feasible when a given spot of the magneto-optical recording medium is inverted by magnetization with respect to the direction of initialization caused by laser beam irradiation and application of the biased magnetic field. Also, beam which has irradiated the magneto-optical recording medium.
A conventional recording and reproducing device for the aforesaid magneto-optical card is described below, with reference being made to FIGS. 8-11. Here, however, illustration of a magnetic field generator for application of a biased magnetic field is omitted.
In a recording and reproducing device shown in FIG. 8 first a magneto-optical card 21 is placed under an optical head 22 and is moved repetitively in the direction of the arrow Y at a high speed. The optical head 22 is properly moved in the direction perpendicular thereto (direction indicated by the arrow X). Then a laser beam 24 having passed an objective lens 23 of the optical head 22 moves super-fast along the Y-direction irradiating the magneto-optical recording medium of the magneto-optical card 21 and also moves properly along the X-direction for two-dimensional, scanning. Thus, by irradiation with the laser beam 24, a given piece of information can be recorded as well as reproduced at a given spot on the magneto-optical recording medium. A plurality of tracks are then formed along the Y-direction, and information is recorded along these tracks.
In another recording and reproducing device shown in FIGS. 9-11 the magneto-optical card 21 is placed under the optical head 22 and is properly moved along the direction indicated by the arrow Y. The optical head 22 is rotated at a high speed. This optical head 22 has four objective lenses 23 . . . arranged at an equidistant inward of its periphery. The optical system is switched successively for the magneto-optical recording medium to be irradiated continuously or uninterruptedly with the laser beam 24 emitted through the objective lens 23 located above thereof at a given moment. Hence, the laser beam 24 is moving above the magneto-optical recording medium 23 in a circular path, while the magneto-optical card 21 moves properly in the Y-direction for two-dimensional scanning to be accomplished. On the magneto-optical recording medium there are formed a plurality of tracks in the form of parallel arcs, and information is recorded along these tracks. Needless to say, recording or reproducing of information by irradiation with the laser beam 24 is feasible on any spot on the magneto-optical recording medium.
In the above-described recording and reproducing device shown in FIG. 8, however, although the information recording and reproducing speed is determined by the moving speed of the magneto-optical card 21, the mechanism for moving the magneto-optical card 21 has a large mechanical loss, hence it is difficult to increase its speed. This conventional recording and reproducing device has a problem of the access time being too long.
With the recording and reproducing device shown in FIGS. 9-11, the information recording and reproducing speed is determined by the rotary speed of the optical head 22. With this disk-like optical head 22; the acceleration reaches an equilibrium as it rotates, and the small mechanical loss allows increase of the access speed. With this conventional recording and reproducing device, however, frequent switching of the optical system is needed so that the irradiation of the magneto-optical card 21 is done with the laser beam 24 emitted through the objective lens 23 located above the magneto-optical card 21; and thereby controlling the optical system becomes rather complicated.
Also, positioning of the laser beam 24 by moving either the magneto-optical card 21 or optical head 22 is inevitably low in precision, hence the object lens 23 provided in an optical system manipulating mechanism uses a method of varying the position of the objective lens 23 within a small range or of a light deflector for fine adjustment of the spot to be irradiated by the laser beam 24. This optical system manipulating mechanism enables moving the laser beam 24 on the magneto-optical recording medium in a range of several hundreds microns.
In recording information or data, it is a usual practice to divide the information into portions or units of a proper size. In the case of a magneto-optical recording medium such as a floppy disk, this unit is usually called a sector, whose size is 128 bytes-1,024 bytes. With small computers currently in use, it is often the case that the size of one sector is 512 bytes. Since 1 byte is 8 bits, 512 bytes equal 4,096 bits or 64.times.64 bits when expanded two-dimensionally. Hence, if 1 bit of data can be recorded in a 1.6.times.1.6 micron spot on a magneto-optical recording medium, the data equivalent of 1 sector (512 bytes) can be recorded in a 102.4.times.102.4 micron region. Actually, however, additional are needed for the sector No. and codes for correcting errors; but even if the volume of data per sector is increased 50% to 79.times.79 bits, a region of 126.times.126 microns is enough for recording a sector. If a recording media of magneto-optical characteristics consisting of vertically-magnetized film should be used, it is well possible to record 1 bit of data in a spot of 1.6.times.1.6 microns.
If the range within which the spot irradiated with the laser beam 24 can be varied by means of the optical system manipulating mechanism to 150 microns in order to access the region of 126.times.126 microns, the center position of the laser 24 in the optical head 22 can be a maximum of EQU (150 microns - (126 microns / 2)=87 microns)
87 microns off with respect to the predetermined data region on the magneto-optical card 21. This means that if the data region is roughly searched for with a precision of 80 microns by moving the magneto-optical card 21 and/or the optical head 22, one sector of data is accessible through variation of the irradiation spot of the laser beam 24 by means of the optical system manipulating mechanism only.
Thus, it is possible that, with a given division of data recorded in a two-dimensional region on the magneto-optical recording medium of the magneto-optical card 21, first the region is roughly searched for by moving the magneto-optical card 21 or the optical head 22 and then recording or reproduction of the data in the particular region by scanning with the laser beam 24 by means of the optical system manipulating mechanism. By this, high speed access becomes feasible and the normally complicated procedure for control of the optical system can be dispensed with.
However, when the optical head 22 being moved for rough searching is stopped, the resulting shock causes the objective lens 23 to vibrate and the accessing by means of the optical system manipulating mechanism is infeasible until stabilization thereof. It is possible to use an actuator-locking mechanism for forcibly fixing the optical head 22 as it is stopped, but this means further complication of the mechanical control mechanism.
When, as an alternative, the optical head 22 is kept fixed and the magneto-optical card 21 alone is moved, vibration of the magneto-optical card 21 has to be taken into consideration.